Whole books have been written on the subject of energy storage alone. In the near future, we will see some dramatic advances in this area of research. Today, most energy storage is accomplished through the use of batteries. This can range from a single PV module and a car battery supplying a few 12VDC loads, to very large and sophisticated backup systems.
Equipment is available from SMA that can provide battery backup in the event of a grid outage. Speak with your local installer to determine the best solution for your needs.